The present invention relates to data signal recording apparatus particularly of the magnetic type and directed to enhancement of preamble or synchronizing signals associated with a leading edge of a recorded data record.
Magnetic recording apparatus, particularly for use with data processing systems, have employed diverse record members and diverse recording and readback apparatus. Most record members have provisions for receiving a plurality of data records. Generally, each data record area is preceded by a set of synchronizing signals for synchronizing readback apparatus for accurately sensing the recorded data record. Such synchronizing signals precede the data transducing operation, hence are termed preamble signals. Such preamble signals are disposed only on one side of each data record for those recording apparatus always scanning the record in the same direction. Such apparatus include magnetic disk apparatus, many magnetic card apparatus, magnetic strips, storage drums, and helical scan magnetic recorders. Some magnetic recording apparatus can scan each data record in either direction. As an example, most magnetic tape units can read in both directions. In such a situation such preamble signals are located at each end of the data record area. In one-half inch tape recorders, for example, the direction of writing is always in the same direction and is termed a forward direction. In such apparatus, the leading portion for recording purposes includes synchronizing signals called a preamble, while signals at the opposite end of the data record area are termed a postamble. In any event, most recording apparatus, particularly those recording apparatus for higher density data recording, employ preamble synchronizing signals for ensuring reliable readback.
All of the synchronizing signals have a marker signal denominating the separation between the synchronizing signals and the data signals. Such a marker signal is necessary to precisely define the beginning of data. It turns out that when reading magnetic records, it is not possible to precisely indicate when synchronizing signals begin. Therefore, it is not possible to rely on counting synchronizing signals for identifying beginning of data.
The single beginning of data mark can take any one of many forms, usually includes a long wave length. With the advent of ever-increasing data recording densities, the areal extent of such a marking signal becomes increasingly small, hence, increasingly susceptible to recording error conditions resulting in missing a beginning a data point. If this one marker signal becomes obliterated or unreadable for one reason or another, all of the data recording in the data record area associated with such marker signal, can become irretrievable. Such loss of data signals should be avoided.